This invention relates to an exterior panel for a motor vehicle. In particular, this invention relates to an exterior body panel for a motor vehicle.
The present invention relates to automotive exterior body components that can be provided with improved dimensional stability, increased structural modulus (stiffness) and strength while increasing surface toughness. At the same time, the exterior body parts can be made with less material, and thus lighter, while achieving the above-improved structural characteristics. In addition, because less material is used, manufacturing costs are reduced.
Hard exterior vehicle parts, such as hoods, quarter panels, truck beds, outside door panels, lift gates, truck lids, bumper beams, and tailgates generally require high dimensional stability, low flexibility, and a low coefficient of thermal expansion. For example, these parts cannot have a high coefficient of linear thermal expansion because they are generally bounded on two or more sides by other parts, with a predetermined gap therebetween. If these parts expand or contract to a large extent, the gap would have to be made larger than desirable to accommodate large expansion on hot days or smaller than desirable to accommodate shrinkage on cold days. Thus, the coefficient of linear thermal expansion for these parts should be less than 20xc3x9710xe2x88x926 inches of expansion per inch of material per degree Fahrenheit (IN/IN)/xc2x0F. In the past, these components have been typically constructed from metal material, such as steel.
Plastics are advantageous over steel in that they are lighter in weight and are not subject to the same degree of deterioration due to oxidation. Thermoset plastics, such as polyester resin molding compounds (SMC and BMC) have also been employed for various hard exterior panel applications, such as in the Corvette automobile. These thermoset materials have been highly reinforced, e.g., with glass fibers or mineral fillers constituting about 40-50% reinforcement material by volume of the total volume of the resultant product, to provide sufficient reinforcement and structural rigidity to suit the application. While adequate impact absorption and low thermal expansion can be achieved with the highly reinforced thermoset plastic material, the high reinforcement makes the resultant panel difficult to paint; requiring several coats and touch-up to achieve an even surface appearance.
Thermoplastics would be an advantageous material in comparison with thermosets for automotive hard exterior panel applications, because thermoplastics have much better ductility and thus much better impact absorption characteristics than thermosets. Thermoplastics would also be preferred because they are inherently easier to recycle, both from scrap material or defect parts during production and from scrapped vehicles that are no longer operational. Furthermore, thermoplastics, and in particular polyolefin thermoplastics, are less expensive than thermoset materials.
However, in contrast to thermosets, thermoplastics have not been widely used for exterior vehicle body components because they have been difficult to mold after being loaded with sufficient amounts of glass fiber and mineral reinforcement fillers. Thus, thermoplastics have not been able to be molded with enough reinforcement material to achieve the required impact strength and dimensional stability (e.g., low coefficient of thermal expansion) for exterior vehicle body parts.
The disadvantages of the prior art may be overcome by providing an exterior panel for a motor vehicle having a coefficient of linear thermal expansion of less than 20xc3x9710xe2x88x926 inches of expansion per inch material per degree Fahrenheit. The exterior panel comprises a rigid structure formed from at least one thermoplastic olefin material and reinforcement particles dispersed within the at least one thermoplastic olefin. The reinforcement particles comprise less than 15% of a total volume of the rigid structure. At least 40% of the reinforcement particles have a thickness less than about 50 nanometers. A decorative coating layer having a least one coloring agent is disposed on the rigid structure.
In a more preferred embodiment, at least 50% of the reinforcement particles have a thickness less than about 20 nanometers. It is also preferred for at least 99% of the reinforcement particles to have a thickness less than about 30 nanometers.